In earthworm

Options

A. Integumentary and pharyngeal nephridia are exonephric
B. Pharyngeal and septal nephridia are exonephric
C. Integumentary and septal nephridia are enteronephric
D. Pharyngeal and septal nephridia are enteronephric

Answer

To answer the question regarding the types of nephredia in earthworms, we can follow these steps:

### Step-by-Step Solution

1. **Identify the Types of Nephredia**:
Earthworms have three types of nephredia based on their position in the body:
- Septal Nephredia
- Pharyngeal Nephredia
- Integumentary Nephredia

2. **Describe Septal Nephredia**:
- They are the largest and well-developed nephredia.
- Located attached to both sides of each intersegmental septum behind the 15th segment.
- There are approximately 40 to 50 septal nephredia arranged in two rows.
- Function: They help in discharging waste products directly into the buccal cavity, making them **enteronephric**.

3. **Describe Pharyngeal Nephredia**:
- Found in pairs in the 4th, 5th, and 6th segments.
- Similar in structure to septal nephredia but lack nephrostomes.
- They have ciliated canals and function similarly to septal nephredia, discharging waste into the buccal cavity and pharynx, thus also being **enteronephric**.

4. **Describe Integumentary Nephredia**:
- Located from the 7th segment to the last segment.
- Smaller than septal nephredia and each nephredium is V-shaped with short straight lobes and twisted loops.
- They have two ciliated canals and number around 200 to 250 per segment, with 2000 to 2500 in the clitellum region.
- Function: They discharge nitrogenous metabolic waste products outside the body through nephrediopores, making them **exonephric**.

5. **Evaluate the Options**:
- **Option 1**: Integumentary and pharyngeal nephredia are exonephric. (Incorrect - Pharyngeal is enteronephric)
- **Option 2**: Pharyngeal and septal nephredia are exonephric. (Incorrect - Both are enteronephric)
- **Option 3**: Integumentary and septal nephredia are enteronephric. (Incorrect - Integumentary is exonephric)
- **Option 4**: Pharyngeal and septal nephredia are enteronephric. (Correct - Both are enteronephric)

6. **Conclusion**: The correct answer is **Option 4**: Pharyngeal and septal nephredia are enteronephric.